Various unsaturated hydrocarbon polymers have been reacted with maleic anhydrides to form a variety of maleic anhydride adducts of unsaturated hydrocarbon polymers. The reactivity of maleic anhydride with many unsaturated hydrocarbon polymers is poor and in some instances, as for example with EPDM rubber, even employment of extensive heating is ineffective. Free radical reactions which graft maleic anhydride onto the unsaturated hydrocarbon polymer have been utilized as alternative routes. Free radical grafting leads to chain scission, crosslinking and solvent grafting if the solvent is sufficiently reactive. The reaction of cyclic carbonyl monomers with the unsaturated hydrocarbon polymer overcomes these aforementioned deficiencies in that the cyclic carbonyl monomers can be reacted with the unsaturated hydrocarbon polymer at moderate temperatures in either the bulk or solution state without the employment of free radical initiators to form novel polymers which are useful as solution viscosifiers.